1. Field of the Invention
The present invention relates to a vehicle wheel attachment dynamically operable to compensate for wheel imbalance.
2. Description of the Prior Art
Various forces acting upon a tire tend to cause wheel imbalance, particularly generally upwardly directed forces produced by road imperfections and bumps. The resulting tire bounce reduces the traction or "footprint" of the tire, causing rider discomfort, increased tire wear, less efficient transfer of propulsive torque from the tire to the road, and changes in wheel angular velocity. There is a consequent loss of fuel economy, impaired vehicle stability, and reduced braking efficiency. Other harmful effects of tire bounce are a reduced ability of the wheel to steer or track in a straight line, poorer traction in snow and ice, a greater tendency to hydroplane in rainy weather, and accelerated deterioration in vehicle front end alignment.
Road hazards typically also produce a lateral force vector which acts against the tire side and tends to prevent proper wheel tracking.
Even in instances in which a road is relatively smooth, forces are inherent in the rolling of a tire which produce wheel imbalance. In this regard, usual balancing of a wheel is done either by taking it off the vehicle and arranging it upon or spinning it in a balancing device, or by hoisting the vehicle and spinning the wheel in place. Small weights are placed on the wheel according to the imbalances detected.
However, when a vehicle is on the road each tire is characteristically slightly flattened or deformed by the weight of the vehicle and the center of gyration of the wheel is no longer coincident with the axis of wheel rotation. This off-center relation introduces a vibration or wheel bounce characterized by the same undesirable consequences as the wheel bounce caused by road irregularities.
Certain wheel covers of the prior art, such as those described in U.S. Pat. No. 3,312,505, issued Apr. 4, 1967 for "Wheel Cover," and in U.S. Pat. No. 4,178,041, issued to me on Dec. 11, 1979 for "Wheel Attached Balancing Device," are made relatively heavy to increase the angular momentum of the wheels to which they are mounted. This has the desirable effect of providing greater resistance to forces tending to change the angular momentum. There is a smaller angular deviation of the wheel axis for any applied force. This has a desirable gyroscopic effect in reducing the adverse consequences of side loads on the tire. However, there is an insufficient compensation for certain other types of wheel imbalance.
In this regard, the wheel covers of the aforementioned patents include a central hub structure and radially extending spokes or sectors arranged to project axially in a shallow conical configuration. This conical configuration tends to flatten into a vertical plane when the associated wheel is rotating at relatively high speeds. as the flattening occurs the sectors pass outwardly against a trim ring mounted to the vehicle wheel. The cover is designed so that movement of the hub structure is directly translated into radial forces upon the sectors. This was intended to aid in holding the trim ring in place upon the wheel, and also was intended to load certain portions of the rim differentially, depending upon the stress being experienced by the associated sectors. This was supposed to reduce vibratory motion occurring from an unbalanced condition of the wheel. Neither of these objectives was satisfactorily accomplished.